Buggy code:
public class ActorConditionEditor extends JSONElementEditor { private static final long serialVersionUID = 799130864545495819L ; private static final String form_view_id = "Form" ; private static final String json_view_id = "JSON" ; private JButton acIcon ; private JTextField idField ; private JTextField nameField ; private JComboBox categoryBox ; private IntegerBasedCheckBox positiveBox ; private IntegerBasedCheckBox stackingBox ; private JTextField roundVisualField ; private JSpinner roundHpMinField ; private JSpinner roundHpMaxField ; private JSpinner roundApMinField ; private JSpinner roundApMaxField ; private JTextField fullRoundVisualField ; private JSpinner fullRoundHpMinField ; private JSpinner fullRoundHpMaxField ; private JSpinner fullRoundApMinField ; private JSpinner fullRoundApMaxField ; private JSpinner abilityHpField ; private JSpinner abilityApField ; private JSpinner abilityMoveCost ; private JSpinner abilityUseCost ; private JSpinner abilityReequipCost ; private JSpinner abilityAttackCost ; private JSpinner abilityAttackChance ; private JSpinner abilityDamageMinField ; private JSpinner abilityDamageMaxField ; private JSpinner abilityCriticalSkill ; private JSpinner abilityBlockChance ; private JSpinner abilityDamageResistance ; public ActorConditionEditor ( ActorCondition ac ) { } @ Override public void insertFormViewDataField ( JPanel pane ) { } public class ActorConditionFieldUpdater implements FieldUpdateListener { @ Override public void valueChanged ( JComponent source , Object value ) { ActorCondition aCond = ( ( ActorCondition ) ( target ) ) ; if ( source == ( idField ) ) { aCond . id = ( ( String ) ( value ) ) ; ActorConditionEditor . this . name = aCond . getDesc ( ) ; aCond . childrenChanged ( new ArrayList < com . gpl . rpg . atcontentstudio . model . ProjectTreeNode > ( ) ) ; frame . editorChanged ( ActorConditionEditor . this ) ; } else if ( source == ( nameField ) ) { aCond . display_name = ( ( String ) ( value ) ) ; ActorConditionEditor . this . name = aCond . getDesc ( ) ; aCond . childrenChanged ( new ArrayList < com . gpl . rpg . atcontentstudio . model . ProjectTreeNode > ( ) ) ; frame . editorChanged ( ActorConditionEditor . this ) ; } else if ( source == ( acIcon ) ) { aCond . icon_id = ( ( String ) ( value ) ) ; aCond . childrenChanged ( new ArrayList < com . gpl . rpg . atcontentstudio . model . ProjectTreeNode > ( ) ) ; ActorConditionEditor . this . icon = new ImageIcon ( aCond . getProject ( ) . getIcon ( ( ( String ) ( value ) ) ) ) ; frame . editorChanged ( ActorConditionEditor . this ) ; acIcon . setIcon ( new ImageIcon ( aCond . getProject ( ) . getImage ( ( ( String ) ( value ) ) ) ) ) ; acIcon . revalidate ( ) ; acIcon . repaint ( ) ; } else if ( source == ( positiveBox ) ) { aCond . positive = ( ( Integer ) ( value ) ) ; } else if ( source == ( stackingBox ) ) { <START_BUG> aCond . positive = ( ( Integer ) ( value ) ) ; <END_BUG> } else if ( source == ( categoryBox ) ) { aCond . category = ( ( ActorCondition . ACCategory ) ( value ) ) ; } else if ( source == ( roundVisualField ) ) { if ( value == null ) { if ( ( aCond . round_effect ) != null ) { aCond . round_effect . visual_effect = null ; if ( isEmpty ( aCond . round_effect ) ) { aCond . round_effect = null ; } } } else { if ( ( aCond . round_effect ) == null ) { aCond . round_effect = new ActorCondition . RoundEffect ( ) ; } aCond . round_effect . visual_effect = ( ( String ) ( value ) ) ; } } else if ( source == ( roundHpMinField ) ) { if ( value == null ) { if ( ( aCond . round_effect ) != null ) { aCond . round_effect . hp_boost_min = null ; if ( isEmpty ( aCond . round_effect ) ) { aCond . round_effect = null ; } } } else { if ( ( aCond . round_effect ) == null ) { aCond . round_effect = new ActorCondition . RoundEffect ( ) ; } aCond . round_effect . hp_boost_min = ( ( Integer ) ( value ) ) ; } } else if ( source == ( roundHpMaxField ) ) { if ( value == null ) { if ( ( aCond . round_effect ) != null ) { aCond . round_effect . hp_boost_max = null ; if ( isEmpty ( aCond . round_effect ) ) { aCond . round_effect = null ; } } } else { if ( ( aCond . round_effect ) == null ) { aCond . round_effect = new ActorCondition . RoundEffect ( ) ; } aCond . round_effect . hp_boost_max = ( ( Integer ) ( value ) ) ; } } else if ( source == ( roundApMinField ) ) { if ( value == null ) { if ( ( aCond . round_effect ) != null ) { aCond . round_effect . ap_boost_min = null ; if ( isEmpty ( aCond . round_effect ) ) { aCond . round_effect = null ; } } } else { if ( ( aCond . round_effect ) == null ) { aCond . round_effect = new ActorCondition . RoundEffect ( ) ; } aCond . round_effect . ap_boost_min = ( ( Integer ) ( value ) ) ; } } else if ( source == ( roundApMaxField ) ) { if ( value == null ) { if ( ( aCond . round_effect ) != null ) { aCond . round_effect . ap_boost_max = null ; if ( isEmpty ( aCond . round_effect ) ) { aCond . round_effect = null ; } } } else { if ( ( aCond . round_effect ) == null ) { aCond . round_effect = new ActorCondition . RoundEffect ( ) ; }

Fix:
aCond . stacking = ( ( Integer ) ( value ) ) ;